( 12 ) United States Patent
`Choi et al .
`
`( 10 ) Patent No . :
`( 45 ) Date of Patent :
`
`US 9 , 748 , 076 B1
`Aug . 29 , 2017
`
`US009748076B1
`
`DEŽ @ ( * ) Notice :
`
`( 54 ) APPARATUS FOR FREQUENCY TUNING IN
`A RF GENERATOR
`( 71 ) Applicant : Advanced Energy Industries , Inc . ,
`Fort Collins , CO ( US )
`( 72 ) Inventors : Myeong Yeol Choi , Fort Collins , CO
`( US ) ; Denis Shaw , Fort Collins , CO
`( US ) ; Mike Mueller , Loveland , CO
`( US ) ; Jeffrey Roberg , Longmont , CO
`( US ) ; Steve Jordan , Berthoud , CO
`( US )
`@ ( 73 ) Assignee : Advanced Energy Industries , Inc . ,
`Fort Collins , CO ( US )
`Subject to any disclaimer , the term of this
`patent is extended or adjusted under 35
`U . S . C . 154 ( b ) by 0 days .
`( 21 ) Appl . No . : 15 / 133 , 461
`( 22 ) Filed :
`Apr . 20 , 2016
`( 51 ) Int . Ci .
`H05B 31 / 26
`( 2006 . 01 )
`HO1J 37 / 32
`( 2006 . 01 )
`( 52 ) U . S . CI .
`CPC . . . HOIJ 37 32183 ( 2013 . 01 ) ; HOIJ 37 3299
`( 2013 . 01 ) ; HOIJ 37 / 32155 ( 2013 . 01 )
`Field of Classification Search
`CPC . . . . . . . . . . HO1J 37 / 32813 ; HO1J 37 / 32146 ; HO1J
`37 / 32183
`( Continued )
`References Cited
`U . S . PATENT DOCUMENTS
`5 , 543 , 689 A
`8 / 1996 Ohta et al .
`6 , 020 , 794 A
`2 / 2000 Wilbur
`( Continued )
`
`( 58 )
`
`( 56 )
`
`EP
`FR
`
`FOREIGN PATENT DOCUMENTS
`0935406 A2
`8 / 1999
`2895169 A1 6 / 2007
`( Continued )
`
`OTHER PUBLICATIONS
`Clemente , Gianluigi , “ European Office Action and Extended Search
`Report re Application No . 09724338 . 0 ” , Jul . 21 , 2014 , p . 9 Pub
`lished in : EP .
`
`( Continued )
`Primary Examiner — Douglas W Owens
`Assistant Examiner — Wei Chan
`( 74 ) Attorney , Agent , or Firm — Neugeboren O ' Dowd PC
`( 57 )
`ABSTRACT
`A radio - frequency ( RF ) generator is provided that includes
`an exciter , a power amplifier , a filter , a sensor , and a
`frequency - tuning subsystem . The frequency - tuning subsys
`tem includes a non - transitory , tangible , machine - readable
`medium containing instructions to perform a method that
`includes receiving an impedance trajectory of the plasma
`load ; receiving a reference point in
`a complex - reflection
`coefficient plane , the reference point lying on a reference
`vector passing through the reference point and the origin ;
`receiving , from the sensor , a measured impedance of the
`plasma load ; determining a measurement angle between a
`reference vector and a line passing through the reference
`point and a point in the complex - reflection - coefficient plane
`corresponding to the measured impedance ; scaling the mea
`surement angle by a predetermined constant to produce a
`frequency step ; adding the frequency step to the initial
`frequency to produce an adjusted frequency ; and causing the
`exciter to generate a signal oscillating at the adjusted fre
`quency .
`
`18 Claims , 11 Drawing Sheets
`
`- 100
`
`WWW
`
`RF Generator
`105
`
`Output
`Power
`
`- - - - - 1
`Match
`1
`Network
`110
`
`= sha
`
`Plasma
`Processing
`Chamber
`115
`
`RENO EXHIBIT 2023
`Advanced Energy v. Reno, IPR2021-01397
`
`

`

`US 9 , 748 , 076 B1
`Page 2
`
`( 58 )
`
`Field of Classification Search
`USPC . . . . . . . . . . . 315 / 111 . 21 ; 156 / 345 . 44 ; 455 / 114 . 3 ,
`455 / 125 , 107 , 114 . 2
`See application file for complete search history .
`
`( 56 )
`
`References Cited
`U . S . PATENT DOCUMENTS
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`1
`/ 2009 Kalvitis et al .
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`11 / 2010 Van Zyl
`8 , 040 , 068 B2
`10 / 2011 Coumou et al .
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`E
`7
`8 , 576 , 013 B2 11 / 2013 Coumou
`8 , 674 , 606 B23 / 2014 Carter et al .
`8 , 781 , 415 B1 *
`7 / 2014 Coumou . . . . . . .
`8 , 952 , 765 B22 / 2015 Fish , II et al .
`9 , 041 , 471 B2
`5 / 2015 Coumou
`9 , 214 , 901 B2
`12 / 2015 Owen
`9 , 294 , 100 B2
`3 / 2016 Van Zyl
`2006 / 0066247 AL
`3 / 2006 Koshiishi et al .
`2006 / 0262889 Al 11 / 2006 Kalvaitis et al .
`2009 / 0237170 A1
`9 / 2009 Van Zyl
`2010 / 0194195 Al
`8 / 2010 Coumou et al .
`2011 / 0148303 Al 6 / 2011 Van Zyl et al .
`2012 / 0152914 Al
`6 / 2012 Matsuura
`2013 / 0169359 A
`7 / 2013 Coumou
`2013 / 0214683 Al 8 / 2013 Valcore et al .
`2013 / 0222055 Al 8 / 2013 Coumou et al .
`2014 / 0028389 Al
`1 / 2014 Coumou
`2014 / 0028398 A1 *
`1 / 2014 Owen . . . . . . . . . . . . . . .
`2014 / 0062305 Al
`3 / 2014 Klein et al .
`2014 / 0097908 AL
`4 / 2014 Fisk , II et al .
`2014 / 0155008 A1 *
`6 / 2014 Van Zyl . . . . . . . . . . . . H01J 37 / 32155
`455 / 120
`455 / 120
`
`HO3H 7 / 40
`330 / 149
`
`HO3F 3 / 193
`330 / 276
`
`??
`JP
`??
`WO
`
`2014 / 0220913 A18 / 2014 Coumou et al .
`2014 / 0361690 A1 * 12 / 2014 Yamada . . . . . . . . . . . . H01J 37 / 32091
`315 / 111 . 21
`2015 / 0270104 A1 9 / 2015 Van Zyl
`FOREIGN PATENT DOCUMENTS
`6 / 1997
`09161994 A
`4 / 1999
`02884605 B2
`2 / 2006
`2006054148 A
`418593 B
`1 / 2001
`2013099133 A1
`7 / 2013
`OTHER PUBLICATIONS
`Gill , David Alan , “ Response to European Office Action re Appli
`cation No . 09724338 . 0 " , Feb . 10 , 2015 , p . 15 , Published in : EP .
`The Korean Intellectual Property Office , “ Korean Office Action re
`Application No . 1020107021902 " , Jan . 12 , 2012 , p . 3 , Published in :
`KR .
`TIPO , “ Taiwan Office Action re Application No . 102144318 ” , Dec .
`29 , 2015 , p . 13 , Published in : TW .
`Phu , Sanh D . , " Office Action re U . S . Appl . No . 14 / 094 , 520 ” , May
`12 , 2015 , p . 27 , Published in : US .
`O ' Dowd , Sean R . , “ Response to Office Action re U . S . Appl . No .
`14 / 094 , 520 " , Sep . 14 , 2015 , p . 7 , Published in : US .
`Fernandez , Pedro C . , " Office Action re U . S . Appl . No . 14 / 320 , 268 ” ,
`Feb . 19 , 2016 , p . 26 , Published in : US .
`Gruber , Stephen S . , “ Response to Office Action re U . S . Appl . No .
`14 / 320 , 268 ” , Jun . 20 , 2016 , p . 10 , Published in : US .
`Jung , Jong Han , “ International Search Report re Application No .
`PCT / US09 / 037001 ” , Oct . 16 , 2009 , Published in : PCT .
`Nickitas - Etienne , “ International Preliminary Report on Patentabil
`ity re Application No . PCT / US2013 / 072748 ” , Jun . 18 , 2015 , p . 6 ,
`Published in : CH .
`Mitrovic , Bayer , “ International Search Report and Written Opinion
`re Application No . PCT / US2013 / 072748 ” , Feb . 25 , 2014 , p . 9 ,
`Published in : AU .
`Rabbani , Firoozeh , “ International Search Report and Written Opin
`ion re Application No . PCT / US2015 / 037607 ” , Sep . 21 , 2015 , p . 12 ,
`Published in : AU
`Detering , Frank , “ PCT International Search Report and Written
`Opinion ” , Jun . 20 , 2017 , p . 9 , Publisher : PCT , Published in : PCT .
`* cited by examiner
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 1 of 11
`
`US 9 , 748 , 076 B1
`
`Plasma Processing Chamber 115
`
`100
`
`Match i Network 1
`110
`
`- - - - - -
`
`Output Power
`
`RF Generator 105
`
`FIG . 1
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 2 of 11
`
`US 9 , 748 , 076 B1
`
`105
`
`-
`
`Output Power
`
`Filter
`
`215
`
`Power Amplifier
`
`210
`
`Exciter
`
`205
`
`Sensor
`
`220
`
`
`
`Frequency - Tuning Subsystem 225
`
`
`
`Load - Characterization Module 226
`
`
`
`Frequency Control
`
`230
`
`
`
`
`
`Characterization Data Store 227
`
`
`
`Frequency - Step Generator 228
`
`FIG . 2
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 3 of 11
`
`US 9 , 748 , 076 B1
`
`300
`
`-
`
`Imag ( T )
`
`+ 1
`
`# + 1 ? Real ( T )
`
`305
`
`340
`
`310
`
`V
`
`| 335 335
`
`330
`
`Ref
`
`1
`
`x
`
`UMeas
`
`325
`
`FIG . 3
`
`315
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 4 of 11
`
`US 9 , 748 , 076 B1
`
`Receive impedance trajectory
`of plasma load as a function of frequency
`405
`
`400 400
`
`Receive reference point
`410
`
`Receive impedance measurement of
`plasma load from sensor
`415
`
`Determine measurement angle
`420
`
`Scale measurement angle
`to compute frequency step
`425
`
`Add frequency step to initial frequency to
`produce adjusted frequency
`430
`
`Set exciter to generate adjusted frequency
`435
`
`FIG . 4
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 5 of 11
`
`US 9 , 748 , 076 B1
`
`Receive impedance trajectory
`of plasma load as a function of frequency
`405
`
`500
`
`Receive reference point
`410
`
`Receive impedance measurement of
`plasma load from sensor
`415
`
`Determine measurement angle
`420
`
`Scale measurement angle
`to compute frequency step
`425
`
`Add frequency step to initial frequency to
`produce adjusted frequency
`430
`
`Set exciter to generate adjusted frequency
`435
`
`FIG . 5
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 6 of 11
`
`US 9 , 748 , 076 B1
`
`Receive impedance trajectory
`of plasma load as a function of frequency
`405
`
`- 600
`
`n
`
`Receive reference point
`410
`
`Receive impedance measurement of
`plasma load from sensor
`415
`
`Determine measurement angle
`420
`
`Scale measurement angle
`to compute frequency step
`425
`
`Add frequency step to initial frequency to
`produce adjusted frequency
`430
`
`Set exciter to generate adjusted frequency
`435
`
`No
`
`Threshold reached ?
`605
`
`Yes
`Stop frequency adjustment
`610
`
`FIG . 6
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 7 of 11
`
`US 9 , 748 , 076 B1
`
`7 + 1 ? Real ( T )
`
`320
`
`305
`
`310
`
`Oref
`
`700
`
`Imag ( 1 )
`
`FIG . 7
`
`315
`
`710
`
`720
`
`705
`
`715
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 8 of 11
`
`US 9 , 748 , 076 B1
`
`Receive impedance trajectory
`of plasma load as a function of frequency
`405
`
`- 800
`
`Receive reference point
`410
`
`Receive impedance measurement of
`plasma load from sensor
`415
`
`Determine measurement angle and
`subtract detune angle from it
`805
`
`Scale resulting difference
`to compute frequency step
`810
`
`Add frequency step to initial frequency to
`produce adjusted frequency
`430
`
`Set exciter to generate adjusted frequency
`435
`
`FIG . 8
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 9 of 11
`
`US 9 , 748 , 076 B1
`
`Receive impedance trajectory
`of plasma load as a function of frequency
`405
`
`900
`
`Receive reference point
`410
`
`Receive impedance measurement of
`plasma load from sensor
`415
`
`Determine measurement angle and
`subtract detune angle from it
`805
`
`Scale resulting difference
`to compute frequency step
`810
`
`Add frequency step to initial frequency to
`produce adjusted frequency
`430
`
`Set exciter to generate adjusted frequency
`435
`
`FIG . 9
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 10 of 11
`
`Receive impedance trajectory
`of plasma load as a function of frequency
`405
`
`US 9 , 748 , 076 B1
`
`1000
`
`UUUUULTY
`
`Receive reference point
`410
`
`Receive impedance measurement of
`plasma load from sensor
`415
`
`Determine measurement angle and
`subtract detune angle from it
`805
`
`Scale resulting difference
`to compute frequency step
`810
`
`Add frequency step to initial frequency to
`produce adjusted frequency
`430
`
`Set exciter to generate adjusted frequency
`435
`
`No
`
`Threshold reached ?
`1005
`
`Yes
`Stop frequency adjustment
`1010
`
`FIG . 10
`
`

`

`U . S . Patent
`
`Aug . 29 , 2017
`
`Sheet 11 of 11
`
`US 9 , 748 , 076 B1
`
`1100
`
`INPUT
`
`OUTPUT
`
`NONVOLATILE
`MEMORY
`1120
`
`PROCESSING
`COMPONENT 1
`
`PROCESSING
`COMPONENT N
`
`PROCESSING 1126
`
`1112 DISPLAY
`
`FPGA 1127
`
`RAM 1124
`
`TX / RX
`
`TX / RX
`N
`
`1128
`
`FIG . 11
`
`

`

`US 9 , 748 , 076 B1
`
`5
`
`APPARATUS FOR FREQUENCY TUNING IN
`A RF GENERATOR
`BACKGROUND
`
`load , the measured impedance lying along the received
`impedance trajectory ; determining a measurement angle
`between the reference vector and a line passing through the
`reference point and a point in the complex - reflection - coef
`ficient plane corresponding to the measured impedance , as
`Field
`expressed in terms of complex reflection coefficient ; scaling
`the measurement angle by a predetermined constant to
`The present disclosure relates generally to radio - fre -
`produce a frequency step ; adding the frequency step to the
`quency ( RF ) generators and , more specifically , to appara
`initial frequency to produce an adjusted frequency ; and
`tuses and techniques for tuning the frequency of an RF
`generator that supplies power to a plasma processing cham - 10 causing the exciter to generate a signal oscillating at the
`ber to change the impedance of the plasma load in a desired
`adjusted frequency .
`Another aspect may be characterized as the method
`manner .
`Background
`including repeating iteratively the receiving , from the sen
`In plasma processing , a radio - frequency ( RF ) generator is
`sor , a measured impedance , the determining , the scaling , the
`used to supply power to the plasma load . Today ' s advanced 15 adding , and the causing , the initial frequency in each itera
`plasma processes include ever more complicated recipes and
`tion subsequent to a first iteration being the adjusted fre
`recipe - changing procedures in which load ( plasma ) imped
`quency produced during an immediately preceding iteration .
`ance dynamically changes . This can make it challenging to
`Yet another aspect may be characterized as the method
`match the source impedance of the RF generator with the
`including producing the frequency step by subtracting a
`load impedance of the plasma for efficient power transfer . 20 predetermined detuning angle from the measurement angle
`Such impedance matching can be performed using a match
`and scaling the difference by a predetermined constant .
`ing network , but this approach is relatively slow in the
`BRIEF DESCRIPTION OF THE DRAWINGS
`context of modern short - duration plasma processes . An
`alternative approach is to adjust the frequency of the RF
`FIG . 1 is a block diagram of a plasma processing system
`generator , which alters the impedance of the plasma load . 25
`“ Plasma load , ” in this context , includes the plasma itself and
`in accordance with an embodiment of this disclosure ;
`any matching network . Such an approach has the potential
`FIG . 2 is a block diagram of a RF generator in accordance
`to be much faster than adjusting a matching network . It is
`with an embodiment of this disclosure ;
`also possible to combine the two techniques ( one or more
`FIG . 3 is an illustration of a complex - reflection - coeffi
`matching networks and frequency tuning ) .
`30 cient plane in accordance with an embodiment of this
`Conventional frequency - tuning algorithms struggle with
`disclosure ;
`optimizing parameters for these advanced plasma processes
`FIG . 4 is a flowchart of a method for tuning the frequency
`because both frequency stability and rapid frequency tuning
`of a RF generator in accordance with an embodiment of this
`are required simultaneously . There is , therefore , a need in
`disclosure ;
`the art for an improved apparatus for frequency tuning in an 35
`FIG . 5 is a flowchart of a method for tuning the frequency
`RF generator .
`of a RF generator in accordance with another embodiment of
`this disclosure ;
`SUMMARY
`FIG . 6 is a flowchart of a method for tuning the frequency
`of a RF generator in accordance with yet another embodi
`Exemplary embodiments of the present invention that are 40 ment of this disclosure ;
`FIG . 7 is an illustration of a complex - reflection - coeffi
`shown in the drawings are summarized below . These and
`other embodiments are more fully described in the Detailed
`cient plane in accordance with an embodiment of this
`Description section . It is to be understood , however , that
`disclosure ;
`there is no intention to limit the invention to the forms
`FIG . 8 is a flowchart of a method for tuning the frequency
`described in this Summary of the Invention or in the 45 of a RF generator in accordance with an embodiment of this
`Detailed Description . One skilled in the art can recognize
`disclosure ;
`that there are numerous modifications , equivalents , and
`FIG . 9 is a flowchart of a method for tuning the frequency
`alternative constructions that fall within the spirit and scope
`of a RF generator in accordance with another embodiment of
`of the invention as expressed in the claims .
`this disclosure ;
`An aspect may be characterized as a radio - frequency ( RF ) 50
`FIG . 10 is a flowchart of a method for tuning the fre
`quency of a RF generator in accordance with yet another
`generator that includes an exciter that generates a signal
`oscillating at an initial frequency , a power amplifier that
`embodiment of this disclosure ; and
`amplifies the signal to produce an amplified oscillating
`FIG . 11 is a block diagram depicting physical components
`signal , a filter that filters the amplified oscillating signal to
`that may be used to implement a frequency - tuning subsys
`produce an output signal that supplies power to a plasma 55 tem in accordance with an embodiment of this disclosure .
`load in a plasma processing chamber , a sensor that senses at
`least one property of the plasma load , and a frequency
`DETAILED DESCRIPTION
`tuning subsystem .
`The frequency - tuning subsystem includes a non - transi
`An apparatus for frequency tuning in a radio - frequency
`tory , tangible , machine - readable medium encoded with 60 ( RF ) generator can provide both stability and rapid tuning if
`instructions to perform a method that includes receiving an
`( 1 ) the frequency of the RF generator is adjusted in the
`impedance trajectory of the plasma load as a function of
`correct direction ( up or down ) at each frequency - adjustment
`exciter frequency ; receiving a reference point in a complex
`iteration and ( 2 ) the frequency step ( adjustment in fre
`reflection - coefficient plane , the reference point lying on a
`quency ) is made adaptive , such that a large step is applied
`reference vector that passes through the reference point and 65 when the current frequency is far from the target frequency
`an origin of the complex - reflection - coefficient plane ; receiv -
`( promotes rapid tuning ) , and a small step is applied when the
`ing , from the sensor , a measured impedance of the plasma
`current frequency is close to the target frequency ( promotes
`
`

`

`US 9 , 748 , 076 B1
`
`228 . Load - characterization module 226 receives or assists in
`stability ) . As explained further below , in some embodiments
`acquiring preliminary load - impedance characterization data
`the target frequency corresponds to minimum I ( complex
`associated with a particular plasma load to produce an
`reflection coefficient ) , and , in other embodiments ( detuned
`impedance trajectory ( see Element 305 in FIG . 3 ) . The data
`embodiments ) , the target frequency corresponds to an inten
`tionally selected T other than the minimum I .
`5 obtained during load characterization can be stored in char
`acterization data store 227 . Frequency - step generator 228
`One key to achieving these objectives is to characterize
`performs the computations to generate frequency adjust
`the impedance of the plasma load as a function of generator
`ments ( frequency steps ) that are fed to exciter 205 via
`frequency beforehand . Such characterization can be accom
`frequency control line 230 . Specific illustrative frequency
`plished through analysis of circuit models , through prelimi -
`nary testing ( measurements ) , or a combination of these 10 tuning algorithms performed by frequency - tuning subsys
`techniques . For example , the impedance of the plasma load
`tem 225 are discussed below in connection with FIGS . 3 - 10 .
`can be measured at each of a number of different frequencies
`As discussed further below , in some embodiments , the
`over a particular range ( e . g . , 13 MHz to 14 MHz ) . Such
`objective is to adjust the frequency of exciter 205 , thereby
`preliminary characterization can produce an “ impedance
`changing the impedance of the plasma load , in a manner that
`trajectory ” for the load as a function of generator frequency . 15 minimizes I
`( i . e . , that achieves a
`I as close to zero as
`This impedance trajectory can be expressed in terms of
`possible ) . As mentioned above , the frequency that achieves
`complex reflection coefficient I , as discussed further below .
`this minimum I may be termed the target frequency . As
`Once this impedance trajectory is known , it is possible to
`those skilled in the art understand , an ideal complex reflec
`compute the correct frequency - step direction ( positive or
`tion coefficient of zero corresponds to a matched condition
`negative ) and appropriate frequency - step size at each fre - 20 in which the source and plasma - load impedances are per
`quency - adjustment iteration , as explained further below .
`fectly matched . In other embodiments , the objective is not
`Referring now to the drawings , where like or similar
`minimum 1 . Instead , frequency - tuning subsystem 225 inten
`elements are designated with identical reference numerals
`tionally tunes exciter 205 to generate a frequency other than
`throughout the several views , and referring in particular to
`the one that produces minimum T . Such an embodiment may
`FIG . 1 , it is a block diagram of a plasma processing system
`25 be termed a " detuned ” implementation .
`in accordance with an embodiment of this disclosure . In
`FIG . 3 is an illustration of a complex - reflection - coeffi
`FIG . 1 , plasma processing system 100 includes RF generator
`cient ( T ) plane 300 in accordance with an embodiment of
`105 , which outputs power to a plasma ( not shown ) in plasma
`this disclosure . FIG . 3 illustrates concepts relating to the
`processing chamber 115 directly or indirectly via one or
`algorithms carried out by frequency - tuning subsystem 225 .
`more matching networks 110 . Herein , the term “ plasma 30
`In FIG . 3 , complex reflection coefficients T are plotted
`load ”
`is used to mean the plasma in plasma processing
`within a unit circle . As those skilled in the art will recognize ,
`chamber 115 in combination with any matching network 110
`T can also be plotted on a standard Smith Chart . In FIG . 3 ,
`that might be present , depending on the particular embodi -
`the horizontal axis corresponds to the real part of I , and the
`ment ( some embodiments do not include a matching net -
`vertical axis corresponds to the imaginary part of T . FIG . 3
`work 110 ) . In other words , " plasma load ” refers to the entire 35 shows a pre - characterized impedance trajectory 305 of the
`load that the output of RF generator 105 drives .
`plasma load expressed in terms of T . As discussed above ,
`FIG . 2 is a block diagram of RF generator 105 in
`impedance trajectory 305 can be determined in advance
`accordance with an embodiment of this disclosure . RF
`through analysis , testing performed with the aid of load
`generator 105 includes exciter 205 , power amplifier 210 ,
`characterization module 226 via an appropriate user inter
`filter 215 , sensor 220 , and frequency - tuning subsystem 225 . 40 face , or a combination thereof . Those skilled in the art will
`Exciter 205 generates an oscillating signal at RF frequen -
`recognize that impedance trajectory 305 will not always
`cies , typically in the form of a square wave . Power amplifier
`intersect origin 340 , as shown in FIG . 3 . In some embodi
`210 amplifies the signal produced by exciter 205 to produce
`ments , impedance trajectory is shifted such that it does not
`an amplified oscillating signal . For example , in one embodi -
`pass through origin 340 , in which case the minimum achiev
`ment power amplifier 210 amplifies an exciter output signal 45 able I is greater than zero .
`of 1 mW to 3 kW . Filter 215 filters the amplified oscillating
`Frequency - step generator 228 of frequency - tuning sub
`signal to produce a signal composed of a single RF fre -
`system 225 also receives , via a suitable user interface , a
`reference point 315 in I plane 300 . In some embodiments ,
`quency ( a sinusoid ) .
`Sensor 220 measures one or more properties of the plasma
`reference point 315 is specified in terms of a reference angle
`load in plasma processing chamber 115 . In one embodiment , 50 320 and a magnitude ( distance of the reference point from
`sensor 220 measures the impedance Z of the plasma load .
`origin 340 ) . As those skilled in the art will recognize , origin
`Depending on the particular embodiment , sensor 220 can be ,
`340 corresponds to the point with coordinates ( 0 , 0 ) at the
`for example and without limitation , a VI sensor or a direc
`center of the unit circle in I plane 300 . Those skilled in the
`tional coupler . Such impedance can
`alternatively be
`art also understand that it is straightforward to compute
`expressed as a complex reflection coefficient , which is often 55 Cartesian coordinates for reference point 315 , given refer
`denoted as “ T ” ( gamma ) by those skilled in the art . Fre
`ence angle 320 and a magnitude M . Specifically , the coor
`quency - tuning subsystem 225 receives impedance measure -
`dinates can be computed as Real ( T ) = M cos ( O Ref + I ) and
`ments from sensor 220 and processes those measurements to
`Imag ( T ) = M
`sin ( Orert ) , where the reference angle Oper
`produce frequency adjustments that are fed to exciter 205
`( 320 ) is expressed in radians and M is a positive real number
`via frequency control line 230 to adjust the frequency 60 less than or equal to unity . In other embodiments , reference
`generated by exciter 205 . Illustrative frequency - tuning algo -
`point 315 is received in terms of Cartesian coordinates ( real
`rithms that are performed by frequency - tuning subsystem
`part and imaginary part ) .
`225 are discussed in detail below in connection with FIGS .
`Once the reference point has been received , frequency
`step generator 228 of frequency - tuning subsystem 225 can
`3 - 10 .
`In the embodiment shown in FIG . 2 , frequency - tuning 65 determine a reference vector 310 . Reference vector 310 is a
`subsystem includes load - characterization module 226 , char -
`line that passes through reference point 315 and origin 340
`acterization data store 227 , and frequency - step generator
`of T plane 300 , as indicated in FIG . 3 . One important
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`US 9 , 748 , 076 B1
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`a measurement angle 330 for the measurement point 325
`function of reference vector 310 is to divide I plane 300 into
`corresponding to the received impedance measurement . At
`two regions , one in which the frequency associated with a
`Block 425 , frequency - step generator 228 then scales mea
`measurement point 325 is higher than the optimum fre -
`surement angle 330 by a predetermined constant K
`to
`quency ( the region in FIG . 3 to the right of reference vector
`5 compute a frequency step . Note that , as method 400 com
`310 ) and one in which the frequency associated with a
`mences , exciter 205 generates an oscillating RF signal at an
`measurement point 325 is lower than the optimum frequency
`initial frequency . At Block 430 , frequency - step generator
`( the region in FIG . 3 to the left of reference vector 310 ) . By
`228 adds the frequency step to the initial frequency gener
`determining in which of the two regions a measurement
`ated by exciter 205 to produce an adjusted frequency . At
`point 325 lies , a frequency adjustment in the correct direc -
`tion ( positive or negative ) can be made at each and every 10 Block 435 , frequency - tuning subsystem 225 , via frequency
`frequency - adjustment iteration ( see FIGS . 5 - 6 and 9 - 10
`control line 230 , signals exciter 205 to generate an oscillat
`ing RF signal at the adjusted frequency , which causes the
`below ) .
`Those skilled in the art will recognize that reference
`impedance of the plasma load to change to a value closer to
`vector 310 need not be an axis of symmetry with respect to
`the desired load impedance .
`impedance trajectory 305 , as expressed in terms of T . The 15
`FIG . 5 is a flowchart of a method 500 for tuning the
`choice of where to place reference point 315 , which in turn
`frequency of a RF generator in accordance with another
`determines reference vector 310 , is somewhat arbitrary ,
`embodiment of this disclosure . The method shown in FIG .
`though a choice should be made that makes possible the
`5 is performed by frequency - tuning subsystem 225 . Method
`calculation of useful measurement angles 330 that support
`500 is similar to method 400 , except that , in method 500 , the
`effective frequency tuning . That means choosing a reference 20 operations performed at Blocks 415 , 420 , 425 , 430 , and 435
`point 315 such that the measurement angle 330 decreases as
`( frequency tuning ) are repeated iteratively in a loop . Those
`the exciter 205 frequency approaches the target frequency , a
`skilled in the art will recognize that , in this embodiment , the
`measurement angle 330 of zero corresponding to the target
`initial exciter 205 frequency at each iteration subsequent to
`frequency .
`the first iteration is the adjusted frequency produced during
`Sensor 220 provides frequency - tuning subsystem 225 25 the immediately preceding iteration . This may be expressed
`with frequent measurements of the impedance of the plasma
`mathematically as Adjusted Frequency ( or Next Frequency )
`load in plasma processing chamber 115 . Measurement point
`= Current Frequency + Frequency Step . In this embodiment ,
`325 in FIG . 3 represents one illustrative impedance mea
`minimum T at or very near zero can be achieved as the
`surement on impedance trajectory 305 , as expressed in terms
`algorithm converges to the optimum frequency .
`of T ( complex reflection coefficient ) in T plane 300 . Fre - 30
`FIG . 6 is a flowchart of a method 600 for tuning the
`quency - step generator 228 of frequency - tuning subsystem
`frequency of a RF generator in accordance with yet another
`225 determines , for measurement point 325 , a measurement
`embodiment of this disclosure . The method shown in FIG .
`angle 330 with respect to reference vector 310 . This mea -
`6 is performed by frequency - tuning subsystem 225 . Method
`surement angle 330 is scaled by a predetermined constant of
`600 is similar to methods 400 and 500 , except that method
`proportionality K ( the loop gain ) to produce a frequency step 35 600 adds a T threshold 335 ( a value between 0 and 1 ) for
`( i . e . , an amount by which the frequency generated by exciter
`terminating frequency adjustment , once the frequency gen
`205 is to be adjusted ) . K is selected based on the frequency
`erated by exciter 205 has reached a value that produces a
`resolution of the frequency - tuning algorithm ( e . g . , 1 kHz vs .
`plasma - load impedance that is deemed sufficiently close to
`1 Hz ) , the resolution of the measurement - angle calculations ,
`the desired value . Method 600 proceeds as in method 500
`and the particular impedance characteristics of the plasma 40 through Block 435 . At Decision Block 605 , frequency - step
`load . The loop gain K can be different from recipe to recipe ,
`generator 228 determines whether I at the current measure
`and it can change within a given recipe in accordance with
`ment point 325 is smaller in magnitude than threshold 335
`changes in the load impedance , in which case the multiple
`( shown in FIG . 3 as an equal - magnitude circular neighbor
`values of K employed in the recipe can be stored in a lookup
`hood surrounding origin 340 ) . If so , frequency - step genera
`table . The calculated frequency step is added to the initial or 45 tor 228 terminates exciter 205 frequency adjustments at
`current exciter frequency to produce an adjusted frequency
`Block 610 . In this situation , the exciter 205 frequency is
`that is closer to the desired or target frequency correspond
`maintained at its current value , and no further adjustments to
`ing to the desired plasma - load impedance . Frequency - tuning
`the frequency are made . Otherwise , if the magnitude of I at
`subsystem 225 then causes exciter 205 , via frequency con -
`the current measurement point 325 is greater than or equal
`trol line 230 , to generate a RF signal at the adjusted 50 to threshold 335 , control returns to Block 415 , and another
`frequency .
`iteration of exciter 205 frequency adjustment is performed .
`Also shown in FIG . 3 is a I threshold 335 , the function
`FIGS . 7 - 10 introduce another family of embodiments in
`of which will be explained below in connection with FIG . 6 .
`which the objective is not minimum 1 . As mentioned above ,
`FIG . 4 is a flowchart of a method 400 for tuning the
`these embodiments may be termed a “ detuned ” implemen
`frequency of a RF generator in accordance with an embodi - 55 tation . In some implementations , a detuned configuration is
`ment of this disclosure . The method shown in FIG . 4 is
`ch